A wireless device is required to maintain a good communication quality, and power of its output signal should be controlled such that it does not interfere with another wireless device. In particular, a mobile wireless device is required to control power with a high precision in comparison to a fixed wireless device because a distance between mobile devices and their antenna orientations thereof are frequently changed.
Due to temperature characteristics of a semiconductor used in a power detector, the amplitude of an output signal is changed according to ambient temperature, regardless of the input power level. Therefore, there is a need to regulate the change in the output signal due to a change in temperature.
Thus, in one example of the related art, temperature compensation is performed by supplying a bias to a detection diode through a Zener diode having a positive temperature coefficient.
Further, in another example, temperature compensation is executed by configuring a balanced type circuit by using a diode and positive and negative power sources with the same capacity.
However, in the above examples, circuit components in the wireless device should be selected in such a manner that a temperature coefficient of a Zener diode and that of a detection diode are mutually canceled out. However, the Zener diode and the detection diode have different structures manufactured in different processes, and thus, it is often difficult to manufacture those components with characteristics sufficient to mutually cancel out the temperature coefficients of the Zener diode and the detection diode. This makes it difficult to produce a circuit with an appropriate combination of the above mentioned components, which leads to a degradation of a production yield. Further, this causes the power consumption to increase because of the amount of a current flowing through the Zener diode.
In addition, as the positive and negative power sources are required to have the same capacity, a production of the detection device becomes more complex and the related cost becomes more expensive. A power detection technology is widely used in wireless devices such as mobile phones, toys, etc., and thus the cost reduction also becomes an important issue in this technology. Moreover, the conventional technology imposes another problem that a change in the power source voltage leads to a change in a detected power output.